Ferrosilicon as a deoxidizing, inoculating and/or alloying agent



United States Patent 3,278,294 FERROSILICON AS A DEOXIDIZING, INOCULAT-ING AND/0R ALLOYING AGENT Klaus Feldmann, Hermnlheim, near Cologne, andKlaus Frank, Knapsack, near Cologne, Germany, assignors to KnapsackGriesheim Aktiengesellschaft, Knapsack, near Cologne, Germany, acorporation of Germany No Drawing. Filed Apr. 11, 1963, Ser. No. 272,197Claims priority, application Germany, May 2, 1962, K 46,630 8 Claims.(Cl. 75-24) The present invention relates to an additive of aferrosilicon alloy suitable for use as a deoxidizing, inoculating and/oralloying agent for increasing the silicon content of steel or cast iron.

It is known that the silicon content of steel or cast iron can beincreased by means of crushed or ground commercial ferrosiliconcontaining 25 to 90% by weight silicon. Ferrosilicon, which preferablycontains 75% by weight silicon, can also be used as an inoculating agentin the manufacture of cast iron with spherically separated graphite, theferrosilicon being added as a germforming agent after treatment withmagnesium. Independently of the silicon content of the alloy used, theferrosilicon is employed in lumpy or comminuted form and often in sievedgrain fractions having a size, for exam-pie, of O to 3 mm.; 2 to 6 mm.;2 to 10 mm.; 3 to 20 mm. or 20 to 40 mm.

Ferrosilicon of such grain size is more especially used:

(1) As a deoxidizing agent, i.e.,

(a) for the deoxidation by precipitation, wherein ferrosilicon is addedto the liquid steel to react directly with the oxygen dissolved (in theform of FeO) in the steel with the resultant formation of (b) for thedeoxidation by diffusion, wherein the slag which has formed on the steelbath in the furnace and contains considerable amounts of metal oxides ismost frequently reduced with ferrosilicon. The slag is thereby deprivedof metal oxides (especially FeO) and thus enabled again to absorb FeOascending in the steel for the reason that an equilibrium is formedbetween the FeOcontent in the slag and that in the steel, theequilibrium being determined by the FeO-content of the slag, that is tosay the proportion of FeO in liquid steel increases as does theFeO-content in the slag;

(2) As an alloying agent for a plurality of steel grades of which twoshould be specifically mentioned:

(a) dynamo steel and transformer steel (b) heat resistant steels;

(3) As an alloying agent for increasing the silicon content in castiron. The ferrosilicon is preferably introduced into the casting pan;

(4) As an inoculating agent in the casting of iron, the ferrosiliconbeing added to the liquid cast iron shortly before it is being castwhich influences the separation of graphite in the manner desired;

(5) As a slag reducing agent. Ferrosilicon may be used as a slagreducing agent even without a deoxidation by diffusion as specifiedunder (1b) above being associated therewith. Ferrosilicon will be usedwith advantage as a slag reducing agent or as an absolute reducing agentwhenever oxides, for example, of chromium, molybdenum, vanadium,tungsten or other high grade metals are intended to be reduced.

It is known, however, that ground ferrosilicon absorbs gases, forexample hydrogen during storage. The ferrosilicon is therefore calcinedbefore it is added to steel, the calcination being intended on the onehand to preheat the alloy addition and, on the other, to expell thegases absorbed especially during storage. The gas absorption is afunction of the surface area of the ground ferrosilicon grains whichappears to indicate that comminuted ferrosilicon contains an increasedproportion of gas.

Ground ferrosilicon offers the further disadvantage of beinginsufficiently stable to abrasion during transport or under any otherstress. It may be assumed that during the solidification of ferrosiliconthe impurities contained therein crystallize predominantly at the grainboundaries and that the alloy structure therefor exhibits instability toabrasion. The conventional application of crushed and groundferrosilicon is in most cases burdened with the loss of the finestportions thereof. These are either retained in the slag or are blownaway by the thermal buoyancy above the iron melt. Furthermore, thesefinest ferrosilicon portions undergo favored oxidation as early as theyare introduced into the melt bath by the air, which is hot from furnaceradiation. Still further, they include a larger proportion of impuritieswith a reduced content of silicon. It is obvious that the accuracy inthe calculation of the ferrosilicon addition for use as an alloying ordeoxidizing agent is thereby reduced.

It is also known that lumpy or ground ferrosilicon may decompose bydisintegration even without perceivable external influences beingobserved.

We have now unexpectedly found that ferrosilicon grains having a hard,smooth and rounded-off surface area are free from the disadvantagesmentioned above. According to an especially advantageous embodiment ofthe present invention the ferrosilicon grains have a spherical orglobular shape and are surrounded by a thin but gas-impermeable andstrongly adhering oxide skin. In addition to the hard grain surface, itis their spherical or globular shape which contributes to a veryeffective protection against abrasion. The granules having anapproximately sperical shape can be used in grain sized within thelimits, for example, of 0.5 to 2 mm.; 2 to 6 mm.; 6 to 10 mm.; or 10 to25 mm. Grains having a size greater than here indicated often lack thespherical shape, but they are scarcely less abrasion-resistant and gasimpermeable.

The grain surface which is smooth, round and enveloped by an oxide filmis preferably hardened by chilling as more fully described below, whichsubstantially avoids the separation of impuries at the grain boundaries,with the resultant formation of an alloy having a completely uniformcomposition. The ferrosilicon particles used in accordance with thepresent invention therefore do not include segregations such asotherwise observed in ground ferrosilicon as regards the content ofsilicon and contaminants. Such segregations could result in the additionof ferrosilicon to steel or cast iron failing to produce accurately thepredetermined effect.

The ferrosilicon granules used in accordance with the present inventionare prepared from the melt in known manner by atomization or spraying.The ferrosilicon melt which may have been prepared, for example, byelectrothermal means is atomized or sprayed with the aid of water,steam, air, nitrogen, or the like under a pressure within the range of1.01 to 13 atmospheres absolute (0.01 to 12 atmospheres gauge).

The atomization of the ferrosilicon melt in known manner with the helpof water or steam has previously been burdened with the prejudice thatthese media could enter into reaction with the melt and thusconsiderably increase the gas content thereof, especially the hydrogencontent thereof, with the resulting granulated ferrosilicon becominguseless for the iron and steel industries. We have now unexpectedlyfound that the contrary is the case. The

atomization by means of water favors immediately a superficial hardeningand the formation of a thin but tight and solidly adhering oxide layer,which avoids any further reaction or dilfusion that would be associatedwith an increase of the gas content. Contrary to all expectation, theferrosilicon granules obtained from the melt by atomization exhibit atmost a hydrogen content the same as the melt before atomization.

:In preparing granulated ferrosilicon by atomizing an iron-silicon alloymelt, care should be taken that the resulting granular material isobtained in rather compact form. This is achieved by spraying the liquidiron-silicon melt in a jet not thicker than 40 mm. in diameter andchilling the jet very rapidly to temperatures far below the meltingpoint of iron. Granulated material having a solid massive internalstructure should be prepared not only on the ground that compactgranular material exhibits a greater stability but also and above all onthe ground that hollow and accordingly lighter weight material may bediflicult to introduce into steel below the covering slag layer.

Instead of by atomization, the rounded-off ferrosilicon particles canalso be prepared in known manner from the melt by directly transformingit into granulated material on a granulating disc, water being here thepreferred agent for comminuting the melt and chilling it. Thecomminuting and/or chilling agents, which include, for example, water,steam, air and nitrogen or the like, are used under a pressure withinthe range of about 0.01 to 20 atmospheres gauge pressure) and forced,for example, to pass through nozzles. The granulating step may also becarried out by replacing the disc with a granulating groove. Theferrosilicon melt intended to be atomized or granulated should have atemperature of 1200 to 1600 C.

The granulated ferrosilicon material having a spherical or globularshape and a smooth surface covered by a tight oxide skin which isused'in accordance with the present invention as an alloying,inoculating or deoxidizing agent, can also be prepared as follows: theferrosilicon particles prepared in known manner by grinding solidferrosilicon are passed in a manner known as such, if desired underpressure and with the aid of an atomizing agent, through a heating zone,for example a flame zone, the ferrosilicon particles being melted roundat least superficially on passing that zone and allowed to solidify in acooling or chilling zone following the heating zone.

Granulated ferrosilicon material which has been prepared with the use ofwater or steam as the atomizing agent or with the use of water as thechilling agent, should be dried in known manner. The drying should takeplace at temperatures which are not too high so as to ensure that theoxide skin formed on the individual ferrosilicon particles is notsubstantially enlarged but merely strengthened. The material may besubjected, for example, to a direct continuous current drying process,wherein the hottest temperature is produced at those places where theferrosilicon is moist. The continuous current drying ensures that theindividual grains are heated to a temperature not exceeding 1000 C. Careshould also be taken during the drying step that heating or drying gasesare used in which the partial pressure of steam is fairly low. Thus, itis of advantage to use very pure carbon monoxide (more than CO) as theheating gas. This process can be carried out in the manner describedabove as a calcining drying process at relatively high temperatures.Alternatively, the material may be dried, for example, by indirectheating at relatively low temperatures, for example, at to 200 C., butin this event the oxide skin is only slightly strengthened.

As already mentioned above, the granulated ferrosilicon particles usedin accordance with the present invention offer the particular advantageof having a thin and tightly adhering oxide skin which in conjunctionwith their hardened surface does not permit the subsequent absorption ofgas.

In other words, the ferrosilicon particles retain their initial gascontent which emanates from the melt without the gas content beingultimately increased due to the external influences during storage. Theadvantage offered thereby is outstanding and obvious. Thus, theferrosilicon can be used immediately in a manner independent fromstorage and without being subjected to an additional calcining step foralloying, inoculating or deoxidizing purposes. In granulated material,which has been prepared from ferrosilicon degassed, for example, bytreating it in vacuo, this low hydrogen content is retained. The risk ofgas bubbles being formed in the melt by the addition of ferrosiliconcontaining too high a proportion of gas, which in most cases has beenabsorbed during storage and which is not expelled during calcination, istherefore substantially reduced. In other words, the use of granulatedferrosilicon having a smooth and hardened surface does no longer resultin the steel quality being specifically impaired by the formation ofso-called flakes due to the hydrogen contained in the ferrosiliconmaterial.

We have also found that granulated ferrosilicon material having aspherical shape and a smooth, hardened surface when used in particles ofidentical size with a defined surface area, undergoes dissolution at auniform rate. This uniform rate of disolution and the uniformdistribution of the silicon content and of the inevitable impuritiesover any ferrosilicon particle enable an extensive automatic control inthe iron and steel-producing industries. The rates of dissolution andhence the effects produced by the ferrosilicon added, which ditfer ineach particular application, can be determined beforehand and, sincethey always take place at the same velocity and with the same efiiciencythe automatic control adapted thereto.

The following tests were conducted to establish the advantages offeredby granulated ferrosilicon obtained by atomizing a ferrosilicon melt.

1) 600 kg. of a ferrosilicon charge of 2060 kg. were granulated with theaid of an annular nozzle under a vapor pressure of 0.5 atmosphere (gaugepressure) to a grain size of 1 to 10 mm., while 1460 kg. solidifiedferrosilicon were crushed and then ground to particles of identicalsize.

TABLE '1 Grain size in mm. Grade 0-0. 5 0. 5-1 1-2 2-4 4-6 6-8 Above 8Crushed or ground ferrosilicon:

Portion of grain, percent 26.0 19. 5 14. 5 12.0 9. 2 8. 3 11.0 Si,percent 69. 8 71.13 72. 9 73. 0 74. 3 74. 6 75. 7 Al, percent. 1. 301.13 0.92 0.85 0.81 0.73 0. 08 Oxides, percen 2. 1 0. 9 0.9 0.8 0.8 0.75 0. 7 Granulated terrosilie Portion of grain, percent 2. 5 6.5 7.032.8 27.2 15.1 10.9 Si, percent 73. 2 72. 9 73. 4 73.1 73. 1 73. 5 73.0Al, percent 0.97 0.95 0. 00 0. 92 0.89 0.91 0. 92 Oxides, percent 2.5 1. 6 1.6 1. 3 1. 3 1. 2 1. 2

The above Table 1 clearly indicates the uniformity of the siliconcontent in all grain sizes and the uniform distribution of theimpurities, identified in the above table by the aluminum content,inasmuch as the granulated material prepared by atomizing moltenferrosilicon is concerned, and it also indicates the correspondingnon-uniformity inasmuch as the crushed and ground ferrosilicon inconcerned.

The data indicated for the oxide film are confirmed by by thedetermination of the total oxides. It can readily be seen that the oxidecontent of granulated ferrosilicon is only slightly greater than that ofthe crushed or ground ferrosilicon.

(2) The resistance to abrasion of granulated ferrosilicon as comparedwith that of crushed ferrosilicon was determined by exposing 50 grams ofeither material in a ball mill under identical conditions to grindingstress. The data obtained represent merely comparative values. Theresistance to abrasion was determined by determining the proportion ofgrains which had been ground after 1, 2, 3 and 4 minutes, respectively,under such heavy stress to a grain size of less than 0.5 mm.

The granulated ferrosilicon additive is prepared by atomizing orspraying a ferrosilicon melt, which may have been produced, for example,by electrothermal means, with the aid of water, steam, lair, nitrogen orthe like under a pressure within the range of 0.01 to 12 atmospheres(gauge pressure), or by directly granulating the ferrosilicon melt on agranulating disc, the agents used for comminuting and/or chilling themelt, which include water, steam, air, nitrogen and the like, beingemployed under a pressure within the range of between 0.01 and 20atmospheres (gauge pressure) and being forced, for example, to passthrough nozzles.

The ferrosilicon melt may also be transformed into granulated form bygranulating it in a granulating groove.

The ferrosilicon melt to be comminuted should have a temperature ofabout 1200 to 1600 C. and it should be degassed in known manner, forexample, by treatment in vacuo before it is transformed into granularform by atomization or granulation.

The resulting granulated ferrosilicon is then freed from adhering waterby subjecting it to a calcining drying step.

According .to a further feature of the present invention Of thegranulated material which had been chilled and therefore had a hardenedsurface and a globular shape only as little as 7.8 or 7.4% had beencomminuted after 4 minutes ofgrinding to a grain size of less than 0.5mm., whereas 62.6 or 48.6% of the crushed ferrosilicon had beencomminuted to a grain size of less than 0.5 mm.

(3) The stability of the granulated material to outdoor influences forexample during storage, was tested by placing 10 grams each ofgranulated ferrosilicon and of crushed ferrosilicon in water at 90 C.and measuring the gas evolved. Absolute values again were not obtained.The test results indicate, however, to the expert the superiorresistance to chemical reactions and/or diffusion phenomena of water orsteam of the granulated material as opposed to the crushed material.

The present invention provides more particularly an additive offerrosilicon suitable for use as a deoxidizing, inoculating and/ oralloying agent for increasing the silicon content in steel or cast iron,the additive consisting of granulated ferrosilicon having a smooth androunded-off, preferably a globular shape and a hard surface produced bychilling. The granulated ferrosilicon is preferably surrounded by anoxide skin and has a massive internal structure.

The ferrosilicon additive generally contains to 90% by weight,preferably 70 to 80% by weight, silicon and it is used in grain sizeswithin the range of about 0.5 to about 25 mm. in diameter.

the granulated ferrosilicon is prepared by grinding solid ferrosiliconwhich is subsequently passed, if desired under pressure and with the aidof an atomizing agent through a heating zone, for example a flame zone,the ferrosilicon particles being melted round at least superficially onpassin that zone and allowed to solidify in a cooling or chilling zonefollowing the heating zone.

The following examples serves to illustrate the inven tion, but it isnot intended to limit the invention thereto.

Example The reduction of slag may serve as an example to describe theadvantage oifered by the granulated ferrosilicon having a smooth androunded-off, preferably a globular shape and a surface area hardened bychilling as compared with ground ferrosilicon.

Slag was reduced as usual while using ferrosilicon, 75% having a grainsize within the limits of 0 to 3 mm. This small grain size had to beused in order to achieve a good distribution of the ferrosilicon overthe slag surface area. Under identical conditions, the slag of 20charges was treated (a) with ground ferrosilicon and (b) with granulatedferrosilicon having the above indicated grain size and composition.

Altogether 1050 kg. ground ferrosilicon were necessary for slagreduction, whereas merely 880 kg. granulated ferrosilicon were requiredto produce the same effect.

The silicon content in the ground ferrosilicon had been determined asbeing 74.5% and the silicon content in the granulated ferrosilicon hadbeen determined as being 73.9%. In other words, 1050 kg. groundferrosilicon corresponding to 782 kg. silicon and 880 kg. granulatedferrosilicon corresponding to 650 kg. silicon had been consumed,respectively.

The degree to which the silicon was utilized had thus been improved byabout 20%.

We claim:

1. A method of deoxidizing liquid steel which comprises adding to saidliquid steel a deoxidizing agent comprising abrasion resistant,granulated ferrosilicon particles of substantially uniform chemicalcomposition, said particles containing from more than 25 to 90 percentby weight silicon, having a massive internal structure, a smooth androunded off surface area hardened by chilling, a grain size within thelimits of about 0.5 to about 25 mm. and being enveloped by agas-impermeable oxide film whereby the particles are resistant toabsorbing gas during storage rendering it unnecessary to preheat themprior to use to expel such gas.

2. A method of inoculating cast iron for influencing the separation ofgraphite which comprises adding to the liquid cast iron shortly beforecasting an inoculating agent comprising abrasion resistant, granulatedferrosilicon particles of substantially uniform chemical composition,said particles containing from more than 25 to 90 percent by weightsilicon, having a massive internal structure, a smooth and rounded offsurface area hardened by chilling, a grain size within the limits ofabout 0.5 to about 25 mm. and being enveloped by a gas-impermeable oxidefilm whereby the particles are resistant to absorbing gas during storagerendering it unnecessary to preheat them prior to use to expel such gas.

3. A method of increasing the silicon content of an alloy selected fromthe group consisting of cast iron and steel which comprises adding tothe liquid alloy an alloying agent comprising abrasion resistant,granulated ferrosilicon particles of substantially uniform chemicalcomposition, said particles containing from more than 25 to 90 percentby weight silicon, having a massive internal structure, a smooth androunded off surface area hardened by chilling, a grain size within thelimits of about 0.5 to about 25 mm. and being enveloped by agas-impermeable oxide film whereby the particles are resistant toabsorbing gas during storage rendering it unnecessary to preheat themprior to use to expel such gas.

4. A method of reducing the metal oxide content of slag which comprisesadding to the liquid slag a slag reducing agent comprising abrasionresistant, granulated ferrosilicon particles of substantially uniformchemical composition, said particles containing from more than 25 to 90percent by weight silicon, having a massive internal structure, a smoothand rounded off surface area hardened by chilling, a grain size withinthe limits of about 0.5 to about 25 mm. and being enveloped by agas-impermeable oxide film whereby the particles are resistant toabsorbing gas during storage rendering it unnecessary to preheat themprior to use to expel such gas.

5. A method according to claim 1 wherein the granulated ferrosiliconparticles contain to percent by weight silicon.

6. A method according to claim 2 wherein the granulated ferrosiliconparticles contain 70 to 80 percent by weight silicon.

7. A method according to claim 3 wherein the granulated ferrosiliconparticles contain 70 to 80 percent by weight silicon.

8. A method according to claim 4 wherein the granulated ferrosiliconparticles contain 70 to 80 percent by weight silicon.

References Cited by the Examiner UNITED STATES PATENTS 1,942,173 5/1932Justheim 7557 2,144,200 6/1939 Rohn 75-57 X 2,527,186 10/1950 Grifiiths7557 FOREIGN PATENTS 777,775 6/1957 Great Britain. 798,269 7/ 8 GreatBritain.

OTHER REFERENCES Alloy Cast Irons Handbook, second edition 1944,American Foundrymens Association, p. 37.

Metals Handbook, 1948 edition, American Society for Met, pp. 338 and515.

DAVID L. RECK, Primary Examiner.

P. WEINSTEIN, Assisnant Examiner.

4. A METHOD OF REDUCING THE METAL OXIDE CONTENT OF SLAG WHICH COMPRISESADDING TO THE LIQUID SLAG A SLAG REDUCING AGENT COMPRISING ABRASIONRESISTANT, A GRANULATED FERROSILICON PARTICLES OF SUBSTANTIALLY UNIFORMCHEMICAL COMPOSITION, SAID PARTICLES CONTAINING FROM MORE THAN 25 TO 90PERCENT BY WEIGHT SILICON, HAVING A MASSIVE INTEERNAL STRUCTURE, ASMOOTH AND ROUNDED OFF SURFACE AREA HARDENED BY CHILLING, A GRAIN SIZEWITHIN THE LIMITS OF ABOUT 0.5 TO ABOUT 25 MM. AND BEING ENVELOPED BY AGAS IMPERMEABLE OXIDE FILM WHEREBY THE PARTICLES ARE RESISTANT TOABSORBING GAS DURING STORAGE RENDERING IT UNNECESSARY TO PREHEAT THEMPRIOR TO USE TO EXPEL SUCH GAS.